Field of the Invention
The present invention relates to a balance of plant (hereinafter simply referred to as ‘BOP’) system of solid oxide fuel cells, a solid oxide fuel cell stack module, and a method for operating solid oxide fuel cells wherein hydrogen and oxygen are reacted with each other by the supply of hydrocarbon fuel to produce electricity therefrom.
Background of the Related Art
Basically, a fuel cell is a device which produces electricity with electrons produced by the reaction of hydrogen and oxygen. If water electrolysis is conducted, in more detail, oxygen and hydrogen are generated from the electrodes, and in this case, the fuel cell makes use of the reverse reaction of the water electrolysis to produce electricity and water from the hydrogen and oxygen. The hydrogen and air (oxygen) are supplied to an anode and a cathode and reacted with an electrolyte to form ions. In the process of forming water through the electrochemical reaction with the produced ions, electrons are produced from the anode and moved to the cathode, thus producing electricity and further generating heat. Unlike general chemical cells (for example, batteries, storage batteries and so on), the fuel cell can continuously produce electricity only if hydrogen and oxygen are supplied thereto.
Electricity is generated from one fuel cell, but the amount of electricity generated is very small if used really. Accordingly, a large number of fuel cells are stacked in series to produce a large amount of electricity therefrom, which is called a fuel cell stack.
The fuel of the fuel cell makes use of pure hydrogen, and otherwise, makes use of hydrogen produced through a process of reforming hydrocarbon like methane, ethanol and so on. On the other hand, the pure hydrogen enhances the efficiency of the fuel cell, but undesirably increases the cost and weight due to the storage of oxygen. Instead of oxygen, accordingly, air is used.
On the other hand, the fuel cell using hydrocarbon as fuel is called a solid oxide fuel cell. Referring schematically to solid oxide fuel cells in the conventional practice, for example, the conventional solid oxide fuel cells include a stack having anodes and cathodes located on both sides thereof and electrolytes provided between the anodes and cathodes to produce electricity through the electrochemical reaction with the hydrogen and oxygen supplied to the anodes and cathodes, a reformer for transforming fuel gas into hydrogen so as to supply the hydrogen to the anodes of the stack, an after burner for heating the reformer and a steam generator, a heater for preheating the air supplied to the cathodes, and the steam generator for supplying steam to the reformer.
According to the solid oxide fuel cells in the conventional practice, the components are connected with each other by means of various pipes and valves, which makes the whole piping configuration undesirably complicated and causes the heat loss in the fluid transmission and heat transmission among the components.
Further, a startup burner is additionally disposed on the outside of the system, which requires separate manufacturing costs and causes low heat efficiencies.
Furthermore, a separate electric heater is provided to preheat the air supplied to the inlets of the cathodes, which reduces the whole heat efficiency.